perf: Replace channel check with atomic bool in tailer.send() (#12976)

pkg/ingester/tailer.go

@@ -4,6 +4,7 @@ import (
 	"encoding/binary"
 	"hash/fnv"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	"github.com/go-kit/log/level"
@@ -46,6 +47,7 @@ type tailer struct {
 	// and the loop and senders should stop
 	closeChan chan struct{}
 	closeOnce sync.Once
+	closed    atomic.Bool
 
 	blockedAt         *time.Time
 	blockedMtx        sync.RWMutex
@@ -74,6 +76,7 @@ func newTailer(orgID string, expr syntax.LogSelectorExpr, conn TailServer, maxDr
 		maxDroppedStreams: maxDroppedStreams,
 		id:                generateUniqueID(orgID, expr.String()),
 		closeChan:         make(chan struct{}),
+		closed:            atomic.Bool{},
 		pipeline:          pipeline,
 	}, nil
 }
@@ -227,17 +230,13 @@ func isMatching(lbs labels.Labels, matchers []*labels.Matcher) bool {
 }
 
 func (t *tailer) isClosed() bool {
-	select {
-	case <-t.closeChan:
-		return true
-	default:
-		return false
-	}
+	return t.closed.Load()
 }
 
 func (t *tailer) close() {
 	t.closeOnce.Do(func() {
-		// Signal the close channel
+		// Signal the close channel & flip the atomic bool so tailers will exit
+		t.closed.Store(true)
 		close(t.closeChan)
 
 		// We intentionally do not close sendChan in order to avoid a panic on

pkg/ingester/tailer_test.go

@@ -17,6 +17,7 @@ import (
 )
 
 func TestTailer_RoundTrip(t *testing.T) {
+	t.Parallel()
 	server := &fakeTailServer{}
 
 	lbs := makeRandomLabels()
@@ -66,6 +67,7 @@ func TestTailer_RoundTrip(t *testing.T) {
 }
 
 func TestTailer_sendRaceConditionOnSendWhileClosing(t *testing.T) {
+	t.Parallel()
 	runs := 100
 
 	stream := logproto.Stream{
@@ -103,6 +105,7 @@ func TestTailer_sendRaceConditionOnSendWhileClosing(t *testing.T) {
 }
 
 func Test_dropstream(t *testing.T) {
+	t.Parallel()
 	maxDroppedStreams := 10
 
 	entry := logproto.Entry{Timestamp: time.Now(), Line: "foo"}
@@ -224,6 +227,7 @@ func Test_TailerSendRace(t *testing.T) {
 }
 
 func Test_IsMatching(t *testing.T) {
+	t.Parallel()
 	for _, tt := range []struct {
 		name     string
 		lbs      labels.Labels
@@ -241,6 +245,7 @@ func Test_IsMatching(t *testing.T) {
 }
 
 func Test_StructuredMetadata(t *testing.T) {
+	t.Parallel()
 	lbs := makeRandomLabels()
 
 	for _, tc := range []struct {
@@ -364,3 +369,21 @@ func Test_StructuredMetadata(t *testing.T) {
 		})
 	}
 }
+
+func Benchmark_isClosed(t *testing.B) {
+	var server fakeTailServer
+	expr, err := syntax.ParseLogSelector(`{app="foo"}`, true)
+	require.NoError(t, err)
+	tail, err := newTailer("foo", expr, &server, 0)
+	require.NoError(t, err)
+
+	require.Equal(t, false, tail.isClosed())
+
+	t.ResetTimer()
+	for i := 0; i < t.N; i++ {
+		tail.isClosed()
+	}
+
+	tail.close()
+	require.Equal(t, true, tail.isClosed())
+}